[GRO] check whether ip_id continuity needs to be checked when two TCP packets are merged.

[Hu, Jiayu]

Hi Cheng,

> -----Original Message-----
> From: jiangheng (G) <jiangheng14 at huawei.com>
> Sent: Saturday, April 15, 2023 10:46 PM
> To: users at dpdk.org; Hu, Jiayu <jiayu.hu at intel.com>; dev at dpdk.org
> Subject: [GRO] check whether ip_id continuity needs to be checked when
> two TCP packets are merged.
> 
> Hi jiayu.hu
> 
> It cannot be guaranteed that 16bit identification field of ip packets in the
> same tcp stream will be continuous.
> Please help check whether ip_id continuity needs to be checked when two
> TCP packets are merged?
> Seems to modify the following code, gro will aggregate better, and work
> better:
> 
> diff --git a/lib/gro/gro_tcp4.h b/lib/gro/gro_tcp4.h index
> 212f97a042..06faead7b5 100644
> --- a/lib/gro/gro_tcp4.h
> +++ b/lib/gro/gro_tcp4.h
> @@ -291,12 +291,10 @@ check_seq_option(struct gro_tcp4_item *item,
>         /* check if the two packets are neighbors */
>         len = pkt_orig->pkt_len - l2_offset - pkt_orig->l2_len -
>                 pkt_orig->l3_len - tcp_hl_orig;
> -       if ((sent_seq == item->sent_seq + len) && (is_atomic ||
> -                               (ip_id == item->ip_id + 1)))
> +       if (sent_seq == item->sent_seq + len)

For atomic packets, the IP ID field is ignored, as it can be set in various ways.
For non-atomic packets, it follows Linux kernel tcp_gro_receive().

Is this change specific to your case? Can you give more details on why it helps?

Thanks,
Jiayu
>                 /* append the new packet */
>                 return 1;
> -       else if ((sent_seq + tcp_dl == item->sent_seq) && (is_atomic ||
> -                               (ip_id + item->nb_merged == item->ip_id)))
> +       else if (sent_seq + tcp_dl == item->sent_seq)
>                 /* pre-pend the new packet */
>                 return -1;